Is it Possible to Build Up an Immunity to Poison Like They Do in the Movies?

In one of my favorite movies, the Princess Bride, the hero Westley challenges Fizzini to a battle of wits. Westley puts a deadly poison, iocane powder in one of two glasses and Fizzini has to choose which one to drink.

Eventually Fizzini chooses and drinks his wine and then keels over dead. It turns out that Westley had tricked him, he had put the iocane in both glasses, but Westley had build up a tolerance of iocane powder so that it wouldn’t kill him. So this raises the question: Is it really possible to build a tolerance for poison? Or is this just a crazy action movie plot point?

Well I don’t know about iocane power specifically, but I have found out that you can build up a tolerance for another kind of poison, arsenic. Arsenic is a toxin that binds to and inactivates proteins that are essential to metabolism. However it can be inactivated in the body by enzymes called metallothionines, and the presence of arsenic can induce liver cells to produce more of these. If small quantities of arsenic are consumed over a period of time, then enzyme production will be induced more often and background levels will increase, thus allowing you to survive a dose of arsenic that would normally be lethal.

In fact there is even a word, mithridatism, which means the phenomenon of partial immunity to poison acquired by taking small doses. Mithridatism was named after Mithridates the Great, King of Pontus from 120 B.C. to 63 B.C. One of the legends of Mithridates VI was that he was worried that someone might try and poison someone of his stature so he created a universal antidote consisting of opium and honey.

The opium and honey would weaken the poison enough that he could take a dose without it killing him and he would then slowly build up a tolerance. Ironically when Mithridates VI was finally defeated by Pompey and in danger of capture by Rome, he allegedly tried to attempt suicide by poisoning himself which of course failed because he had built up an immunity to poison. Instead he had to have one of his servants kill him by sword.

I’m not sure what difference there is between iocane power and arsenic but at least we know that it is possible to build up a tolerance to some poisons. I’m still not sure if I buy this part of the plot though. Do ALL the Dread Pirate Roberts sit around sipping iocane powder to build immunity or is this just a hobby of Westley’s? Because it seems farfetched to be sitting in your boat and thinking, “hmm, if I build up this immunity to iocane powder then later I can trick someone into a battle of wits where I put it in both cups and get them to drink it”. Most pirates would spend their time practicing their sword fighting and cool accents.

NOTE: In no way do I encourage others to try and build up a tolerance to poison. I advise you do not drink arsenic, eat rat poison, drink snake venom or drink orange juice with pulp. (The last one is not poisonous, just really, really gross.)

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